The present invention relates to the recording, storage, and reading of information utilizing low-glide height, high recording density, magneto-optical (xe2x80x9cMOxe2x80x9d) media, particularly rotatable MO storage media, such as in the form of thin film disks, for use with a cooperating transducer and/or sensor head or similar device. More particularly, the present invention relates to a method for treating the deposition surface(s) of such type MO media for enabling operation at very low glide height. The present invention enjoys particular utility in the manufacture of magnetic super-resolution (xe2x80x9cMSRxe2x80x9d)-type and near field recording (xe2x80x9cNFRxe2x80x9d)-type MO media and hybrids thereof, configured as single- or dual-sided first surface magneto-optical (xe2x80x9cFSMOxe2x80x9d)-type media.
In recent years, much research and development of magneto-optical (MO) recording media for use as high density/high capacity memory and data storage and retrieval devices has been carried out. Such media typically comprise a suitable substrate, e.g., of glass, polymer, metal, or ceramic material, coated with a perpendicularly magnetizable film used as a recording medium. Information is recorded within the medium by switching the direction of magnetization of desired portions (i.e., domains) of the perpendicularly magnetizable film. More specifically, for recording information, the recording medium is first initialized by applying to the medium a magnetic field from an externally positioned magnetic field generation device (i.e., external magnetic bias), thereby making the direction of the perpendicular magnetization uniformly upwardly or downwardly facing. A first laser beam of sufficiently high power or intensity from a suitable source, e.g., a laser diode, is then irradiated on desired recording portions of the recording medium in the presence of an externally applied magnetic bias field. As a consequence of the laser beam irradiation, the temperature of the irradiated portions (domains) of the recording medium rises, and when the temperature reaches or exceeds the Curie point of the vertically magnetizable film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. When this state is achieved at the desired recording portions of the medium, and in the presence of the externally biased magnetic field, the direction of the perpendicular magnetization is switched, e.g., from upwardly facing (=digital logic 1 or 0) to downwardly facing (=digital logic 0 or 1, respectively) or vice versa, so as to be aligned with that of the external magnetic field. At the end of a write pulse (i.e., laser pulse), the temperature of the heated recording domain then decreases and eventually returns to room temperature by cessation of the laser beam irradiation thereof. Since the alignment direction of magnetization of the recording media effected by the laser pulse heating to above the Curie temperature is maintained at the lowered temperature, desired information can thus be recorded in the magneto-optical media.
For reading the information stored in the MO media according to the above-described method, the recorded portions of the media are irradiated with a second, linearly polarized laser beam of lower power or intensity than the one used for recording, and light reflected or transmitted from the recorded portions is detected, as by a suitable detector/sensor means. The recorded information is read out by detecting the Kerr rotation angle of the polarization plane of light reflected from the recording layer or the Faraday rotation angle of the polarization plane of light transmitted through the recording layer. More particularly, since the rotation angle of the polarization plane varies depending upon the direction of magnetization of the recorded portions of the media according to the Kerr or Faraday effect, information stored within the media can be read out optically by a differential detector which decodes the polarization-modulated light beam into bits of information.
Conventional MO recording technology typically utilizes a transparent substrate and the polarized, lower intensity laser beam is transmitted through the recording medium layers for reception by the detector/sensor means for measurement of the rotation angle of the transmitted polarized light via the Faraday effect, as explained supra. However, in first surface magneto-optical (FSMO) recording systems, polarized, lower intensity laser beam light is reflected from the MO medium for measurement of the amount of rotation of the plane of the polarized laser light via the Kerr effect, again employing a suitable detector/sensor means. The FSMO type system is advantageous in that, inter alia, opaque substrate materials, e.g., polymers, can be utilized, and dual-sided media are readily fabricated. In addition, FSMO-type media can advantageously utilize such less expensive polymeric substrates with a pre-formatted servo pattern easily formed on the surface thereof by a mastering and injection molding process, therefore not requiring electronic servo as in conventional hard disk drive technology.
In addition to the above-mentioned advantages, the direct irradiation of the MO layer(s) of FSMO-configured media via the front side also results in several other advantages vis-a-vis through-the-substrate illumination, e.g., FSMO systems can utilize head sliders flying over the disk surface by forming the optical and magnetic components integral with the slider, whereby the laser beam is irradiated through the slider body and directly focussed on the MO read-write layer.
The recording density of MO disk types, including magnetic super-resolution (xe2x80x9cMSRxe2x80x9d), near field recording (xe2x80x9cNFRxe2x80x9d), and hybrids thereof, when utilized as FSMO-configured disks, depends, in major respect, on the spot size of the focussed laser beam(s) employed for writing (and reading-out) information stored in the MO medium layer(s). The minimum spot size or diameter d is limited by diffraction according to the relation d=0.5xcex/NA, where xcex is the wavelength of the laser light and NA is the numerical aperture of the objective lens of the focussing system. In MO systems utilizing conventional technology, i.e., wherein laser irradiation of the MO medium layer is through a transparent substrate, head-disk spacings are typically in the range of hundreds of microns. However, as indicated supra, first surface magneto-optical (FSMO) systems utilizing non-transparent substrates can be devised in which a flying head slider integrally incorporates the requisite optical and magnetic components. In systems of such configuration, the laser beam passes through the slider body and is directly focussed on the MO storage medium layer. Near-field optical techniques have been developed for use with such systems in order to overcome the above-mentioned diffraction limit by using a high refractive index material as a solid immersion lens (xe2x80x9cSILxe2x80x9d), which SIL is positioned between the objective lens and the FSMO-configured disk. In such systems, the laser beam spot size or diameter is determined by the aperture size of the SIL, which aperture size can be much smaller than that possible with conventional optical focussing systems.
The spacing, or air-gap, between the SIL and the FSMO-configured disk surface is termed the xe2x80x9cflying heightxe2x80x9d or xe2x80x9cglide heightxe2x80x9d for flying-head recording. In the past, most research on FSMO systems utilizing SIL-type optics was directed towards achieving a flying or glide height of about 5 microinches (127 nm). However, the continuing requirement for greater recording/storage density with good coupling efficiency necessitates further decrease in the flying or glide height of such FSMO-based storage systems. Such systems and media therefor are conventionally termed low glide magneto-optical (xe2x80x9cLGMOxe2x80x9d) or near-field recording (xe2x80x9cNFRxe2x80x9d) systems and media.
Such LGMO or NFR recording media, when fabricated in disk form for rotation about a central axis, can be adapted for use in conventional Winchester, or hard drive, devices as are employed with conventional magnetic recording media. As indicated above, hard drives typically employed for such disk-shaped media utilize flying heads for mounting transducer/sensor devices, etc., thereon, for close positioning thereof adjacent the surface of the recording media. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined small distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Therefore, as in the case of magnetic disks, a protective overcoat layer and a lubricant topcoat layer are typically applied to the disk surface for minimizing scratching and abrasion of the sensor/transducer head and the recording media surface, which can result in an undesirably high wear rate of the head and recording media surface.
A difficulty encountered in the development of wear-resistant, lubricated, ultra-high recording density, FSMO-configured LGMO or NFR media and Winchester-type drives therefor, is the above-mentioned requirement imposed by the impetus for achieving ever-higher density recording, which necessitates even further reduction in the disk-transducer/sensor spacing and mandates good coupling efficiency. The head-to-disk interface (HDI) becomes very critical as head-to-disk spacing is reduced and head fly height decreases. Conventional MO and FSMO media without a protective overcoat and lubricant layer have extremely poor tribological performance, resulting in lack of reliability of MO-based disk drives. In addition, conventional substrate materials, as supplied by their respective manufacturers, comprise surfaces including defects, asperities, etc., of sufficient magnitude and/or dimension as to be incompatible with the requirement for very low head glide height, in that the asperities, defects, etc. of the substrate surface are substantially replicated within the various MO and dielectric layers deposited thereover, including the ultimate, or outermost layer destined to be proximate the head slider.
The above-described problems, including disk crashing during head loading, associated with the requirement for reduced head-to-disk spacing and fly height, are further exacerbated in the case of FSMO-configured LGMO media wherein the optical and magnetic components of the recording system are incorporated into the head slider.
Thus, there exists a need for reliable, high recording density single- and dual-sided FSMO-configured LGMO disks and disk-based devices, which disks allow operation with flying heads at substantially reduced flying or glide heights and which effectively eliminate the problems and drawbacks associated with the conventional technology, i.e., scratching, abrasion, brittleness, increased wear of transducer/sensor head and recording media surfaces, and tendency for crashing during head loading, while advantageously providing good coupling efficiency.
The present invention addresses and solves the problems attendant upon the manufacture and use of high density MO media, including FSMO-configured, disk-shaped LGMO or NFR recording media and hard drives, including magnetic super-resolution (MSR)-type disks and hybrids thereof, while maintaining full compatibility with all mechanical aspects of conventional disk drive technology.
An advantage of the present invention is a method of manufacturing ultra-high recording density, low glide height, FSMO-configured recording/data storage and retrieval media, including NFR, MSR, and hybrid types, for use with flying heads operating at extremely low flying or glide heights, while at the same time exhibiting good coupling efficiency, improved tribological performance and long-term durability.
Another advantage of the present invention is a method of treating the deposition surfaces of substrates for use in the manufacture of ultra-high recording density, FSMO-configured recording/data storage and retrieval media, which surface treatment permits operation of finished MO disks at very low glide or flying head heights.
A further advantage of the present invention is a method of manufacturing FSMO-configured, ultra-high recording density disk-shaped MO media for use in information/data storage and retrieval systems having a flying head slider at a flying or glide height less than about 2 microinches above the disk surface, with reduced wear and increased coupling efficiency.
Still another advantage of the present invention is single- and dual-sided, ultra-high recording density, FSMO-configured information/data storage and retrieval media having substrates including improved deposition surfaces providing improved tribological performance at very low flying head or glide heights.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a method of manufacturing a high recording density magneto-optical (MO) information storage and retrieval medium, comprising the sequential steps of:
(a) providing a substrate comprising at least one deposition surface;
(b) mechanically polishing said at least one deposition surface to reduce the asperity thereof; and
(c) photolytically treating the polished at least one deposition surface to remove contaminants and debris therefrom.
According to embodiments of the present invention, step (a) comprises providing a substrate, e.g., a disk-shaped substrate having a pair of opposed major deposition surfaces, and comprising a material selected from the group consisting of: glass, metal alloys, aluminum (Al), NiP-coated Al, polymers, ceramics, glass-ceramics composites, and glass-polymer composites; step (b) comprises performing a tape burnishing process which, according to a specific embodiment of the present invention, comprises a first step of buffing the at least one deposition surface with a moving tape having a surface coated with finely-dimensioned abrasive particles, followed by a second step of wiping the polished at least one deposition surface with a moving tape having a non-abrasive surface; step (c) comprises photolytically treating, e.g., with UV radiation according to a specific embodiment, the polished at least one deposition surface in an ozone-containing atmosphere, and further contacting the polished at least one deposition surface with an inert gas atmosphere subsequent to the photolytic treatment.
According to embodiments of the present invention, the method comprises the further step (d) of depositing a stacked plurality of layers comprising at least one magneto-optical (MO) layer on the polished at least one deposition surface of the substrate.
According to an embodiment of the present invention, the MO medium is configured as a near field recording-first surface magneto-optical (NFR-FSMO)-type medium and a stacked plurality of layers (i)-(vii) deposited in step (d) comprises, in sequence from the polished at least one deposition surface of the substrate:
(i) a heat sinking and reflective layer;
(ii) a first dielectric layer comprising a material which is substantially transparent to the wavelength(s) of at least one laser beam used for writing and reading-out information stored in the medium;
(iii) an MO auxiliary, writing assist layer comprising a rare earth/transition metal (RE-TM) material;
(iv) an MO read-write layer comprising an RE-TM thermo-magnetic material having perpendicular anisotropy, large perpendicular coercivity, and high Curie temperature;
(v) a second dielectric layer comprising a material which is substantially transparent to the wavelength(s) of at least one laser beam used for writing and reading-out information stored in the medium;
(vi) a thin, abrasion-resistant, protective flash layer overcoat (FLO) over the transparent dielectric layer, the FLO layer being substantially transparent to the wavelength(s) of the at least one laser beam used for writing and reading-out information stored in the medium; and
(g) a thin lubricant topcoat layer over the FLO.
According to particular embodiments of the present invention, the heat sinking and reflective layer (i) comprises aluminum (Al) or an alloy thereof; each of the first and second substantially transparent dielectric layers (ii) and (v) comprises a material selected from the group consisting of SiNx, AlNx, SiOx, and AlOx; the MO auxiliary, writing assist layer (iii) comprises an RE-TM material selected from the group consisting of: TbFe, TbFeCo, and FeCoX, where X is Dy, Gd, or Sm; the MO read-write layer (iv) comprises an RE-TM material selected from the group consisting of: TbFe, TbFeCo, TbDyFeCo, and TbFeCoX, TbDyFeCoX, and DyFeCoX, where X is Al, Y, or Nd; the thin, protective FLO (vi) comprises a carbon-based material selected from the group consisting of: ion beam-deposited carbon, plasma-enhanced chemical vapor deposition (PECVD) carbon, a-CNx, a-CHx, and a-CNxHy; and the thin, lubricant topcoat layer comprises a fluoropolyether or perfluoropolyether (PFPE) material.
According to a further embodiment of the present invention, step (a) comprises providing a substrate including a pair of opposed major deposition surfaces; steps (b) and (c) are performed on each of the pair of major surfaces; and step (d) comprises forming the stacked plurality of layers (i)-(vii) on each of the pair of opposed major deposition surfaces.
According to another embodiment of the present invention, the MO medium is configured as a magnetic super resolution, first surface magneto-optical (MSR-FSMO)-type medium and a stacked plurality of layers (i)-(x) deposited in step (d) comprises, in sequence from the at least one deposition surface of the substrate:
(i) a heat sinking and reflective layer;
(ii) a first dielectric layer comprising a material which is substantially transparent to the wavelength(s) of at least one laser beam used for writing and reading-out information stored in the medium;
(iii) an MO auxiliary, writing assist layer comprising a rare earth/transition metal (RE-TM) material;
(iv) an MO writing layer comprising an RE-TM thermo-magnetic material having perpendicular anisotropy, large perpendicular coercivity, and high Curie temperature;
(v) in the case of magneto-exchange coupling type MSR media, an exchange coupling layer comprising an RE-TM material in contact with the MO writing layer for increasing the recording density of the MO writing layer by replicating the magnetic orientation thereof by exchange coupling and increasing the coupling force between the MO writing layer and a spaced-apart MO read-out layer; or
(vi) in the case of magneto-static coupling type MSR media, a second dielectric layer comprising a material which is substantially transparent to the wavelength(s) of the at least one laser beam used for writing and reading-out information stored in the medium for performing magneto-static coupling between the MO writing layer and a MO read-out layer;
(vii) an MO read-out layer comprising an RE-TM material having a small coercivity and low Curie temperature;
(viii) a third dielectric layer comprising a material which is substantially transparent to the wavelength(s) of the at least one laser beam used for writing and reading-out information stored in the medium;
(ix) a thin, abrasion-resistant, protective flash layer overcoat (FLO) over the third, substantially transparent dielectric layer, the FLO layer being substantially transparent to the wavelength(s) of the at least one laser beam used for writing and reading-out information stored in the medium; and
(x) a thin lubricant topcoat layer over the protective FLO.
According to particular embodiments of the present invention, the heat sinking and reflective layer (i) comprises aluminum (Al) or an alloy thereof; each of the first, second, and third substantially transparent dielectric layers (ii), (vi), and (viii) comprises a material selected from the group consisting of: SiNx, AlNx, SiOx, and AlOx; the MO auxiliary, writing assist layer (iii) comprises an RE-TM material selected from the group consisting of: TbFe, TbFeCo, and FeCoX, where X is Dy, Gd, or Sm; the MO writing layer (iv) comprises an RE-TM material selected from the group consisting of: TbFe, TbFeCo, TbDyFeCo, and TbFeCoX, TbDyFeCoX, and DyFeCoX, where X is Al, Y, or Nd; the exchange coupling layer (v) comprises an RE-TM material comprising GdFeCo; the MO read-out layer (vii) comprises an RE-TM material selected from the group consisting of: GdFeCo and GdFeCoX, where X is Al, Nd, or Y, and GdFeCoXXxe2x80x2, where X is Al, Nd, or Y and Xxe2x80x2 is Cr, Ta, or Nb; the thin, protective FLO (ix) comprises a carbon-based material selected from the group consisting of: ion beam-deposited carbon, plasma-enhanced chemical vapor deposition (PECVD) carbon, a-CNx, a-CHx, and a-CNxHy; and the thin, lubricant topcoat layer comprises a fluoropolyether or perfluoropolyether (PFPE) material.
According to a further embodiment of the present invention, step (a) comprises providing a substrate including a pair of opposed major deposition surfaces; steps (b) and (c) are performed on each of the pair of major surfaces; and step (d) comprises forming the stacked plurality of layers (i)-(x) on each of the pair of opposed major deposition surfaces.
According to yet another aspect of the present invention, single- and dual-sided NFR-FSMO and MSR-FSMO configured MO media fabricated according to the inventive process are provided.
According to still another aspect of the present invention, a low glide height FSMO-configured data/information storage and retrieval system comprises:
a disk-shaped, high recording density FSMO data/information storage and retrieval medium having a surface; and
means for positioning a flying head slider at a fly height less than about 2 xcexcin. away from the disk surface.
Additional advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein only preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as limitative.